For starters, you need to be friends with the person you will invite to the board. Once they've accepted friend request, follow these steps:
1. From your completed games list (or someone elses), open the game you want to analyze by clicking "Analyze in Live." (see screenshot)

2. Once the board loads, find them in the friends tab of live chess, and right click on their name. You will see "Invite to Analysis Board." (see screenshot)

If anyone knows, i'd be grateful!